Apparatus motor control method

ABSTRACT

A method for controlling a motor can suppress an influence of speed variation due to cogging of the motor. The method includes performing a preliminary drive process to output a first driving signal to the motor to move the mechanism, performing the preliminary drive process to output a second driving signal corresponding to a cogging period of the motor to the motor as well as output the first driving signal, to move the mechanism, determining parameters which include an output waveform and output timing of the second driving signal based on a speed of the mechanism in the preliminary drive process, and outputting the second driving signal according to the determined parameters to the motor as well as outputting the first driving signal to the motor in an actual drive process to perform predetermined processing by moving the mechanism.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a motor control method performed by anapparatus.

2. Description of the Related Art

An ink jet recording apparatus and an image reading apparatus areprovided with a motor control device that drives a motor.

The ink jet recording apparatus performs scanning by a recording headusing driving force of the motor. The image reading apparatus performsscanning by a reading unit using the driving force of the motor.

The driving force of the motor includes a torque ripple (coggingtorque), which is transmitted to a carriage via a timing belt. A movingspeed of the carriage is controlled, for example, by using a previouslyprepared speed profile. However, the torque ripple causes speedvariation in the moving speed. The torque ripple is generated at acertain period according to a structure of the motor. To remove aninfluence of the torque ripple, a feed forward control method isdiscussed in which a signal for decreasing the torque ripple is applied.

Japanese Patent Application Laid-Open No. 2006-42525 discusses aconfiguration in which a rectangular pulse which has a same period asthat of the torque ripple is multiplied by a feedback controlled drivingsignal. It is further discussed that the rectangular pulse is applied atpredetermined timing ahead of an opposite phase of the torque ripple.

Japanese Patent Application Laid-Open No. 2006-247997 describes that,when a load given to the motor is relatively large, the influence ofcogging becomes relatively large. In Japanese Patent ApplicationLaid-Open No. 2006-247997, thus, an amount of the load is measured and avoltage (duty value) applied to the motor to null the cogging is changedbased on the amount of the load. Further, a correction value forchanging the voltage and timing for applying the voltage are discussed.Furthermore, it is discussed that the speed variation is measured usingan encoder and the above-described processing is performed until ameasurement result falls below a threshold value.

However, since there are variations in ink jet recording apparatuses, itoften takes a time to adjust the ink jet recording apparatus to reducethe torque ripple. For example, although Japanese Patent ApplicationLaid-Open No. 2006-42525 discusses the timing for applying therectangular pulse but no specific method for acquiring the timing.Japanese Patent Application Laid-Open No. 2006-247997 does not discuss aspecific method for acquiring the timing for applying the voltage tonull the cogging, either. As described above, both of the techniquesneed to perform scanning by a carriage many times to adjust theapparatus, thus taking time for adjustment.

SUMMARY OF THE INVENTION

The present invention is directed to a motor control method.

According to an aspect of the present invention, a method forcontrolling a motor which is used as a driving source in an apparatusthat moves a mechanism by constant speed control includes performing afirst preliminary drive to output a first driving signal to the motor tomove the mechanism, performing a second preliminary drive to output asecond driving signal corresponding to a cogging period of the motorfrom a predetermined phase to the motor as well as output the firstdriving signal to the motor, to move the mechanism, determining thephase of the second driving signal when the output of the second drivingsignal is started based on speeds acquired from the first and secondpreliminary drives, performing a third preliminary drive to output thesecond driving signal from the determined phase to the motor as well asoutput the first driving signal to the motor, to move the mechanism,determining an amplitude of the second driving signal based on a speedacquired from the third preliminary drive, and executing an actual driveby moving the mechanism to perform predetermined processing by startingoutputting the second driving signal to the motor based on thedetermined amplitude and phase as well as outputting the first drivingsignal to the motor.

Further features and aspects of the present invention will becomeapparent from the following detailed description of exemplaryembodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate exemplary embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

FIG. 1 is a perspective view of an ink jet recording apparatus accordingto an exemplary embodiment of the present invention.

FIG. 2 is a perspective view of a carriage according to the exemplaryembodiment.

FIG. 3 is a perspective view of a recording head according to theexemplary embodiment.

FIG. 4 is a cross sectional view of a direct current (DC) motor with abrush.

FIG. 5 illustrates a structure of a control unit of the ink jetrecording apparatus according to the exemplary embodiment.

FIG. 6 illustrates a control configuration of a control unit in the inkjet recording apparatus according to the exemplary embodiment.

FIG. 7 illustrates an operation flow performed by the ink jet recordingapparatus according to the exemplary embodiment.

FIG. 8 illustrates a processing flow of identifying processing accordingto a first exemplary embodiment of the present invention.

FIGS. 9A, 9B and 9C illustrate torque variations (speed variations)according to the first exemplary embodiment.

FIGS. 10A, 10B, and 10C illustrate torque variations (speed variations)according to the first exemplary embodiment.

FIGS. 11A and 11B illustrate the identifying processing according to thefirst exemplary embodiment.

FIG. 12 illustrates the torque variation (speed variation) according tothe first exemplary embodiment.

FIGS. 13A, 13B, and 13C illustrate the identifying processing accordingto a second exemplary embodiment of the present invention.

FIGS. 14A, 14B, 14C, and 14D illustrate the torque variations (speedvariations) according to the second exemplary embodiment.

FIG. 15 illustrates a processing flow of the identifying processingaccording to the second exemplary embodiment.

FIG. 16 illustrates the control configuration of the control unit in theink jet recording apparatus according to another exemplary embodiment ofthe present invention.

FIG. 17 illustrates the control configuration of the control unit in theink jet recording apparatus according to another exemplary embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Various exemplary embodiments, features, and aspects of the inventionwill be described in detail below with reference to the drawings. As oneof examples of electronic devices, an ink jet recording device will beused.

FIG. 1 is a perspective view of an ink jet recording apparatus accordingto the present exemplary embodiment. A carriage 2 mounts a recordinghead 1 and supports a main guide rail 3 and a sub guide rail 4. Thecarriage 2 moves in a direction that crosses a direction in which arecording medium 15 is conveyed.

A timing belt 6 is stretched between a motor pulley 8 connected to amotor 7 that is a driving source and a driven pulley 9 disposed at aposition facing the motor 7. The timing belt 6 is fixed to the carriage2 and a driving force of the motor 7 is transmitted to the timing belt 6to move the carriage 2. A conveyance roller 10 is driven by a conveyancemotor (not illustrated) to convey the recording medium. A dischargeroller 11 discharges the recording medium on which an image is recordedoutside the apparatus.

FIG. 2 is a perspective view of the carriage according to the presentexemplary embodiment. In FIG. 2, an encoder sensor 13 attached to thecarriage 2 reads an encoder scale 14 provided in parallel to a scanningdirection of the carriage 2 and outputs a signal. The signal istransmitted to a central processing unit (CPU) 23 via a flexiblesubstrate 5. The CPU 23 counts a number of sensor signals output fromthe encoder sensor and acquires a position, an amount of movement, and aspeed in the scanning direction of the carriage 2.

FIG. 3 is a perspective view of a recording head according to thepresent exemplary embodiment. On a part of the recording head 1 whichfaces a recording sheet, nozzle arrays 1M, 1C, 1Y, and 1Bk for each inkcolor are disposed. An electric connection unit 20 of the recording head1 is connected to an electric connection unit (not illustrated) of thecarriage 2. The flexible substrate 5 connects the electric connectionunit of the carriage 2 to a substrate on which the CPU 23 is disposed.

FIG. 4 is a cross sectional view of a direct current (DC) motor with abrush. The motor 7 often uses the DC motor for various reasons such asnoise, costs, and control performance. The DC motor with a brushincludes a magnet 15, a rotor 16, a brush 17, a rectifier 18, and amotor housing 19. The rotor 16 which has a rotational structure changesa polarity of a magnetic field by operations of the brush 17 and therectifier 18, and repeats attraction/repulsion between the magnet 15 todrive the motor 7.

When the motor 7 is driven, a periodical pulse of the torque, which isreferred to as the torque ripple or the cogging torque, is generated.The cogging torque refers to a phenomenon in which an attraction forcepulsates depending on a switch of the brush 17, magnetic variation ofthe magnet 15, and a rotation angle φ of the motor 7. The presentexemplary embodiment describes the DC motor with a brush, however, themotor is not limited to this type.

FIG. 5 illustrates a configuration of a control unit of the ink jetrecording apparatus. The control unit controls the inkjet recordingapparatus. The CPU 23 executes a program stored in a read only memory(ROM) 24. The CPU 23 performs image processing, communication processingwith a host computer via an interface (I/F) unit 26, driving control ofthe recording head 1, and a signal output to a pulse width modulation(PWM) calculation unit 108 a. The CPU 23 may be integrated with anapplication specific integrated circuit (ASIC) (not illustrated) whichis an integrated circuit.

The ROM 24 stores programs and control parameters for controlling themotor and the recording head. A random access memory (RAM) 25 is used tostore the program in operation by CPU 23, recorded data transmitted fromthe host computer, and data to be recorded. A non-volatile random accessmemory (NVRAM) 27 stores a correction value described below. The NVRAM27 may be a flush memory or an electronically erasable and programmableread only memory (EEPROM), as long as the memory is a storage unitcapable of storing and reading the data.

A driving circuit 108 includes a PWM calculation unit 108 a and a driver108 b. The PWM calculation unit 108 a inputs the driving signal tocalculate a width of a pulse voltage. The driver 108 b is a drivingcircuit which drives the motor 7 based on a result calculated by the PWMcalculation unit 108 a.

FIG. 6 illustrates a control configuration according to the presentexemplary embodiment. A driving command signal 103 is a driving profileof the carriage 2 which is previously determined by the program. Thedriving profile includes profiles for acceleration control, constantspeed control, and speed reduction control. By following the drivingcommand signal 103, the carriage 2 can move at a desired speed.

A position calculation unit 106 and a speed calculation unit 107 acquireposition information and speed information about the carriage 2respectively based on the signal input from the encoder 12. Theinformation is fed back as a speed signal and a position signal. Controlunits 104 and 105 perform a feedback control (FB control) by using theposition signal, the speed signal, and the driving command signal 103.The FB control performs a predetermined calculation algorithm.

A signal generation unit 100 generates and outputs a period signaldescribed below. A calculation unit 101 calculates parameters such as anamplitude, a frequency, and a phase of the period signal to begenerated. A signal storage unit (information storage unit) 102 storesthe speed information and the position information. The calculation unit101 calculates the parameters of the period signal to be generated usingthe speed information and the position information stored in the signalstorage unit 102.

With the configuration described above, a first driving signal outputfrom the control unit 105 and a second driving signal output from thesignal generation unit 100 are input to the driving circuit 108 to drivethe motor 7.

FIG. 7 illustrates a processing flow performed by the ink jet recordingapparatus. The CPU 23 controls the processing. In step S10, when the CPU23 receives a signal from a host apparatus, the CPU 23 determines acommand included in the signal. When the command is a recording command,the processing proceeds to step S11 and the CPU 23 reads the parameterof the period signal. The read parameter is set to the signal generationunit described below. Then in step S12, the CPU 23 causes the recordinghead to perform scanning and recording.

At this time, the period signal can decrease the influence of thecogging torque of the motor, and thus variation of a scanning speed ofthe recording head can be suppressed. In step S13, the CPU 23 determineswhether the recording operation finishes. When the recording operationdoes not finish (No in step S13), the processing returns to step S12 toperform the recording operation. When the recording operation finishes(Yes in step S13), the processing ends.

In step S10, when the command content is determined as an identifyingcommand, the processing proceeds to step S14 to perform the identifyingprocessing. In the identifying processing, in order to acquire theparameters of the periodic signal, the CPU 23 causes the recording headto perform scanning to acquire the speed information and calculatesparameters of the period signal.

With reference to FIG. 8, the identifying processing according to thefirst exemplary embodiment will be described. The identifying processingis performed to acquire the parameter of the period signal under controlby the CPU 23 as illustrated in FIG. 5. The identifying processingperforms three preliminary drives. The parameters acquired by thepreliminary drives are used when actual driving is executed. FIG. 8illustrates a phase determination process for determining the phase ofthe period signal and an amplitude determination process for determiningthe amplitude of the period signal.

In step S101, the carriage performs scanning according to apredetermined driving command signal and information about the scanningspeed of the carriage at this time is acquired. Then in step S102, aperiod signal of an amplitude value A is applied to the predetermineddriving command signal, and the carriage performs scanning. Informationabout the scanning speed of the carriage at this time is acquired.

Based on the speed information acquired insteps 5101 and 5102, in stepS103, a phase difference between the torque variations caused by thesignal is calculated. More specifically, a difference value between thespeeds is acquired.

Based on a result calculated in step S103, in step S104, a correctionvalue ed of the phase for suppressing the cogging torque is acquired.The correction value ed is a correction value of the phase of thesignal.

In step S105, a period signal in which the correction value ed and theamplitude A are reflected is applied to the predetermined drivingcommand signal. Then, the carriage performs scanning and the informationabout the scanning speed of the carriage is acquired. In step S106, anamplitude ratio is calculated from the amplitude of the speed acquiredin step S105 and that of the speed acquired in step S101. Further, acorrection value Ad is acquired from the calculation result.

In step S107, the correction value ed of the phase and the correctionvalue Ad of the amplitude that are acquired in the processing describedabove are stored in the NVRAM 27 illustrated in FIG. 5.

To acquire the speed information, for example, the information istemporarily stored in the memory (the RAM 25 illustrated in FIG. 5.) Thespeed information is acquired in a predetermined scanning range in aconstant speed control region.

Waveform information stored in the non-volatile memory (the NVRAM 27illustrated in FIG. 5) is read when a power is turned on and set in aregister of the signal generation unit 100. Accordingly, when therecording operation is executed, the period signal is applied based onthe acquired waveform information to suppress the speed variation whenthe carriage performs scanning.

With reference to FIGS. 9A and 9B, the period signal will be described.FIG. 9A illustrates the cogging torque at a position of the carriage ofa printer. According to the exemplary embodiment, one period of thecogging torque is equivalent to eight pulses of the encoder.

FIG. 9B illustrates a waveform of a signal output from the signalgeneration unit 100. The signal generation unit 100 generates the signalsuch that one period of the signal is equivalent to the one period ofthe cogging torque. Thus, the signal generation unit 100 generates thesignal based on a number of the pulses of the encoder equivalent to theone period of the cogging torque and the moving speed of the carriage.

Every printer has a different phase of the cogging torque at apredetermined position. This is because, for example, the printers arenot manufactured to have uniform relations between a position (angle) ofthe rotor 16 in the rotation direction and a position of the carriage inthe scanning direction. Therefore, the phase of the signal does notalways correspond to that of the cogging torque. Thus a phase differencebetween the phase of the signal and that of the cogging torque is avalue unique to each printer.

According to examples illustrated in FIGS. 9A and 9B, the phase in FIG.9B is two pulses behind that in FIG. 9A. In other words, the phase ofthe signal is π/4 behind that of the cogging torque. This phasedifference is the value unique to the printer.

FIG. 9C illustrates the torque of the motor which is applied the periodsignal thereto and drives. The torque of the motor varies correspondingto the period of the period signal. Accordingly, the torque of the motorwhich is applied the period signal thereto and drives has apredetermined phase difference from the torque of the motor to which theperiod signal is not applied as illustrated in FIG. 9A.

With reference to FIGS. 10A, 10B, and 10C, the speed variation of thecarriage will be described. FIG. 10A illustrates the speed informationacquired in step S101. As illustrated in FIG. 10A, the carriage speed isinfluenced by the cogging torque, and thus the torque varies.

FIG. 10B illustrates the speed information acquired in step S102. Asillustrated in FIG. 10B, the carriage speed is influenced by the coggingtorque and the period signal, and thus the speed varies.

FIG. 10C illustrates a difference value between the speed variationillustrated in FIG. 9A and that illustrated in FIG. 9B. The differencebetween the speed variations is influenced by the signal illustrated inFIG. 9B. If the phase of the torque illustrated in FIG. 10C is shiftedand applied to the torque illustrated in FIG. 9A, the torque variationof the carriage can be suppressed. To suppress the torque variation, instep S104, a phase amount ed to be shifted (phase correction value) isacquired. The phase amount ed to be shifted (phase correction value) isacquired based on a position at which the amplitude is maximum in FIG.10A and a position at which the amplitude is minimum in FIG. 10C.

FIG. 11A illustrates scanning by the carriage and a range in which thespeed information is acquired in steps S101 and S102. FIG. 11Billustrates positions where the signal is started to be output.

In FIG. 11A, a width L1 of scanning performed by the carriage in stepsS101 and S102 is smaller than the maximum width L2 of scanning in theink jet recording apparatus. In steps S101 and S102, the speedinformation in a predetermined region (moving range) Q is acquired in aconstant speed control region T of the carriage. As illustrated in FIG.11B, the signal generation unit 100 outputs the period signal in a rangebetween 2000 pulse to 2016 pulse (range of two cogging periods).

As described above, the identifying processing is performed by using theminimum scanning width, and thus a scanning time can be decreased.Further, since the identifying processing is performed by using theminimum data amount, the identifying processing can be performed in ashort time using a less memory capacity.

With reference to FIG. 12, the correction value Ad acquired in step S106will be described. In FIG. 12, a horizontal axis represents an amplitudevalue of the period signal, and a vertical axis represents an amplitudevalue of the speed variation. Accordingly, in FIG. 12, the amplitudevalue Ad when the speed variation is minimum can be acquired bycalculation from speed variation Vref when the amplitude of the periodsignal is zero (the period signal is not applied) and speed variation Vawhen the period signal of the amplitude A is applied. This is because,when the amplitude of the period signal is increased, the speedvariation is decreased at a certain rate.

A second exemplary embodiment will be described. With reference to FIGS.13A, 13B, and 13C, and FIGS. 14A, 14B, 14C, and 14D, the identifyingprocessing will be described. Similar descriptions to that in the firstexemplary embodiment will not be repeated. In the second exemplaryembodiment, it is assumed that transmission characteristic is differentwhen the position of the carriage is largely different. However, thetransmission characteristic is considered to be equal in given vicinity.The one period of the cogging is equivalent to eight pulses of theencoder.

Therefore, as illustrated in FIG. 13A, the constant speed control regionis divided into a plurality (7) of regions (Q1, Q2, Q3, Q4, Q5, Q6, andQ7). For example, it is assumed that the 1000th pulse is a startposition of the constant speed control region, and one region includes800 pulses.

In this case, a pulse location of the region Q1 is 1000th to 1799thpulse. The pulse location of the region Q2 is 1800th to 2599th pulse.The pulse location of the region Q3 is 2600th to 3399th pulse.

A ratio is acquired between an amplitude VrRef 1 illustrated in FIG. 13Bof the speed variation when the period signal is not applied and anamplitude VrSig 1 illustrated in FIG. 13C of the speed variation whenthe period signal is applied. The ratio is acquired in each region (eachmovement range). So that, seven ratios are acquired. Based on the phasecorresponding to the region which has the minimum ratio, the correctionvalue θd is acquired.

FIGS. 14A and 14C illustrate a period waveform in each region. Figuresalong the horizontal axis are values for describing the period and thephase. For example, the period waveform as illustrated in FIG. 14A isapplied from the start position (1000) of the region Q1. FIG. 14Billustrates the speed when the period waveform illustrated in FIG. 14Ais applied. There is no shift of the phase in the region Q1. Output ofthe signal is stopped at an end position 1799 of the region Q1.

The period waveform as illustrated in FIG. 14C is applied from an end ofthe region Q2. FIG. 14D illustrates the speed when the period waveformof FIG. 14C is applied. The period signal whose phase is one pulsebehind as illustrated in FIG. 14C is applied from the start position(1800) of the region Q2. At the end position (2599) of the region Q2,output of the period signal whose phase is one pulse behind is stopped.

In other regions, period signals which have different phrases aresimilarly applied. From the start position of the region Q3, the periodsignal whose phase is three pulses behind is applied. From the startposition of the region Q4, the period signal whose phase is four pulsesbehind is applied. From the start position of the region Q7, the periodsignal whose phase is seven pulses behind is applied.

FIG. 15 illustrates a flow of the identifying processing according tothe second exemplary embodiment. The carriage performs scanningaccording to the predetermined driving command signal. FIG. 15illustrates amplitude ratio acquisition processing for acquiring theamplitude ratio of the speed variations to determine the phase of theperiod signal.

In step S201, information about the scanning speed of this carriage isacquired. In step S202, the period signal which has the amplitude valueA is applied to the predetermined driving command signal and thecarriage performs scanning to acquire the information about the scanningspeed of the carriage.

In step S203, based on the speed information acquired in steps S201 andS202, the amplitude ratios of the regions Q1 to Q7 are acquired.

Then, the region which has the minimum amplitude ratio is specified froma result calculated in step S103. Phase information about the periodsignal applied in the specified region is acquired. In step S204, basedon the phase information, the correction value θd of the phase forsuppressing the cogging torque is acquired. The correction value θd isthe correction value of the phase of the signal. Since a followingprocessing flow is similar to that of the first exemplary embodiment,the descriptions thereof will not be repeated.

Two exemplary embodiments are described, however, the controlconfiguration is not limited to the above-described exemplaryembodiments. As illustrated in FIG. 16, the signal output from thesignal generation unit 100 may be the command signal regarding theposition. Further, as illustrated in FIG. 17, the signal output from thesignal generation unit 100 may be the command signal regarding thespeed.

The above-described exemplary embodiment describes the recordingapparatus which causes the recording head to perform scanning to recorddata in the recording medium as one example of the mechanism. Inaddition to this embodiment, as another embodiment of the mechanism, thepresent invention may be applied to an image reading apparatus thatincludes a reading unit which performs scanning to read an originalimage.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all modifications, equivalent structures, and functions.

This application claims priority from Japanese Patent Application No.2008-333872 filed Dec. 26, 2008, which is hereby incorporated byreference herein in its entirety.

1. A method for controlling a motor which is used as a driving source inan apparatus that moves a mechanism by constant speed control, themethod comprising: performing a first preliminary drive to output afirst driving signal to the motor to move the mechanism; performing asecond preliminary drive to output a second driving signal correspondingto a cogging period of the motor from a predetermined phase to the motoras well as output the first driving signal to the motor, to move themechanism; determining the phase of the second driving signal when theoutput of the second driving signal is started, based on speeds acquiredfrom the first and second preliminary drives; performing a thirdpreliminary drive to output the second driving signal from thedetermined phase to the motor as well as output the first driving signalto the motor, to move the mechanism; determining an amplitude of thesecond driving signal based on a speed acquired from the thirdpreliminary drive; and executing an actual drive by moving the mechanismto perform predetermined processing by starting output of the seconddriving signal to the motor based on the determined amplitude and phaseas well as outputting the first driving signal to the motor.
 2. Themethod according to claim 1, further comprising starting output of thesecond driving signal when the mechanism moves to a predeterminedposition.
 3. The method according to claim 1, further comprisingacquiring speeds of the mechanism in the first and second preliminarydrives in a predetermined movement range.
 4. The method according toclaim 3, further comprising acquiring a difference value between theacquired speeds of the first and second preliminary drives.
 5. Themethod according to claim 4, further comprising determining the phase ofthe second driving signal when outputting of the second driving signalis started based on a phase corresponding to a minimum amount of theacquired difference value and a phase corresponding to a maximum valueof the speed in the first preliminary drive.
 6. The method according toclaim 1, further comprising: outputting the second driving signal from apredetermined phase in each of a plurality of predetermined movementranges in the second preliminary drive; and acquiring each speed of thefirst and second preliminary drives in the plurality of the movementranges.
 7. The method according to claim 6, further comprising acquiringan amplitude ratio between the speed variations in the acquired firstpreliminary drive and the acquired second preliminary drive in eachmovement range.
 8. The method according to claim 7, further comprisingdetermining the phase of the second driving signal when outputting ofthe second driving signal is started based on the acquired amplituderatio.